1. Field of the Invention
The present invention relates to a light quantity adjusting device and an imaging apparatus, and in particular, relates to a light quantity adjusting device that is installed in a video camera and has favorable quality in a blur effect and a ghost shape, and an imaging apparatus using the same.
2. Description of the Related Art
A diaphragm device used as a light quantity adjusting device of an imaging apparatus is generally formed of diaphragm blades. It is known that its opening shape closer to a circle makes more beautiful soft focus effect and what is called a blur effect in a portrait and improves imaging quality. It is also known that because a ghost shape that occurs in a situation against the light is similar to the opening shape formed by the diaphragm blades, the ghost shape improves in quality with the opening shape closer to a circle. Thus, it is always desired that the opening shape formed by the diaphragm blades be closer to a circle as much as possible, thereby improving quality in the blur effect and the ghost shape.
In response thereto, many diaphragm devices installed in imaging lenses for use in high-performance cameras such as single-lens reflex cameras have what is called an iris diaphragm structure that arranges six or eight diaphragm blades circumferentially centering on an optical axis and drives the diaphragm blades so as to move closer to and separate from the optical axis within a plane orthogonal to the optical axis. This structure makes the opening shape formed by the diaphragm blades a hexagon or an octagon, respectively, which are closer to a circle, thereby improving quality in the blur effect and the ghost shape.
It is difficult for small-sized digital still cameras or video cameras mainly for taking moving images to adopt the iris diaphragm structure described above that arranges a plurality of diaphragm blades circumferentially centering on an optical axis and drives the diaphragm blades so as to move closer to and separate from the optical axis within a plane orthogonal to the optical axis, in order to achieve miniaturization, slimming down, and weight reduction.
In view of this, disclosed is a light quantity adjusting device that includes a pair of rectilinear diaphragm blades and a pair of swing diaphragm blades. The device slides the rectilinear diaphragm blades and swings the swing diaphragm blades to adjust the size of a diaphragm opening, thereby making the shape of the formed diaphragm opening nearly a circle or nearly a regular hexagon and reducing space around the diaphragm opening, regardless of the size of the diaphragm opening (see Japanese Patent Application Laid-open No. 2009-115831).
In contrast to the iris diaphragm structure, some light quantity adjusting devices of digital still cameras and video cameras adopt a structure that slides two diaphragm blades along a line orthogonal to an optical axis across a diaphragm opening. This structure is advantageous in achieving miniaturization; because there is no need of large space on both sides of the diaphragm blades (see Japanese Patent Application Laid-open No. 2011-090028).
The Japanese Patent Application Laid-open No. 2009-115831 discloses rectilinear diaphragm blades, swing diaphragm blades, and further a base member including a driving unit for the swing diaphragm blades so as to have a high parts count and to become complicated structure. As a result, although the structure is simplified on the plane parallel to the diaphragm blades, it is difficult to miniaturize the entire imaging apparatus; and there is a problem in restrictions to the shape of a casing.
Although Japanese Patent Application Laid-open No. 2011-090028 discloses no need of large space on both sides of the diaphragm blades but the simple diaphragm blade structure; it must have a linear blade driving lever, similarly making it difficult to miniaturize the entire imaging apparatus, and there is a problem in restrictions to the shape of a casing.